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expert reaction to latest data from the ONS COVID-19 Infection Survey

The Office for National Statistics (ONS) have released the latest data from their COVID-19 Infection Survey.


Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“The latest results from the ONS Covid-19 Infection Survey (CIS) take the estimates of the numbers who would test positive for the virus that can cause Covid-19 up to the week 10-16 October, last week. How depressing or encouraging they look depends on where you are in the UK. Overall, adding up the ONS official reported estimates across the whole UK, the total figure is that a bit over 1.1 million people would have tested positive on a day on the most recent week – that’s 8% higher than the week before. But the position looks different in the different UK countries.

“In England, ONS consider that numbers who would test positive have continued to increase – indeed the official estimate went up by 10% in the latest week compared to the week before, so that around 1 in 55 people (aged 2 and over) in the community population would have tested positive in the latest week. On the face of it, this might not look like a huge increase on the previous week, when the estimated rate was about 1 in 60, but the number testing positive went up by almost 88,000 in a week. It’s this big increase in infections in England that is behind the increase in the UK total, because (as usual) English figures dominate the UK totals because the English population is so much larger than the populations of the other three countries. The current estimated positivity rate in England is higher than it has been ever since the CIS began in April last year, apart from four weeks starting on 27 December 2020 at the very height of the second wave.

“For Wales, ONS say that the numbers who would test positive increased in the two weeks up to 16 October, though they regard the trend during the most recent week as ‘uncertain’. That uncertainty is to quite a considerable extent due to the wider margins of statistical uncertainty in Wales (and also in Northern Ireland, and to a lesser extent Scotland) than in England, and in turn that’s because the number of people swabbed for the CIS in countries other than England is relatively smaller. But it’s clear that the general trend in Wales is one of increase, as it has been since May, and the estimated rate of testing positive there in the most recent week is again the highest it has been since the CIS began there in July 2020. For the most recent week, ONS estimate that about 1 in 45 people in the Welsh community population would have tested positive (with margin of statistical error from 1 in 35 to 1 in 55).

“In both Scotland and Northern Ireland, the trends look more favourable. In Scotland the rate of testing positive decreased again, as it has every week since early September. In the latest week, the estimated positivity rate is about half what it was in early and mid September, at about 1 in 90, though we’ve got to remember that 1 in 90 people, or an estimated 60,100 for the country of Scotland, is still quite a high infection rate. But the continuing downward trend is very encouraging.

“As is often the case for Northern Ireland, the trends are less certain, partly because of the relatively low numbers tested for the CIS, but the overall pattern continues downward, even though ONS regard the trend in the most recent week as uncertain. However, the estimated rate of testing positive there is about 1 in 130, with margin of error from 1 in 95 to 1 in 200. Because of the wide margin of error, we can’t be entirely confident that the positivity rate in Northern Ireland is lower than in Scotland, though it probably is.

“So, overall, the numbers testing positive are rising in England and in Wales, to worryingly high levels, and falling in Scotland and Northern Ireland, though further falls there would be very welcome. The message would seem to be that we must get on with vaccination (booster doses and vaccination for the 12-15 age group in particular), and we’ve got to be more careful on things like mask wearing and being cautious around busy places, whether governments compel us to do so or not.

“For England, ONS give estimates for specific age groups and specific regions, as well as for the whole country, though the more specific estimates are bound to be statistically less precise. In broad terms, the position on age groups is in some ways similar to the position last week, but in some ways more depressing. For the latest week, ONS consider that the percentage testing positive increased in all of the age groups they look at, with the exception of those aged 25-34 where the trend is said to be uncertain. It’s clear that the majority of positive test results are again in the youngest age groups, age 2 years to school year 6, and school years 7 to 11. For secondary school age (school years 7 to 11), ONS are estimating that about 1 in 15 would test positive, and for the younger children (age 2 up to school year 6) they estimate 1 in 25 would test positive. So again the position is that about half the estimated positive tests for the whole of England are in those two age groups up to age about 16 years. (See Further Information below for a technical point about the ONS estimates for these age groups.)

“For the older age groups, estimates range from 1 in 70 testing positive in those aged 35-49 to 1 in 140 testing positive in the 70+ age group. It’s interesting that, again, the highest rate in all these age groups over the age of 16 is in the 35-49 group. It’s been suggested that people in that group could be being infected by their school-age children, though there’s no way to tell that from these CIS figures.

“The regional position in England isn’t encouraging either. ONS estimate that the rate of testing positive increased in five of the nine English regions (North West, the East Midlands, the East of England, London and the South West), levelled off after previous increases in two (West Midlands and the South East), and they say the trend was uncertain in the most recent week in the other two (North East and Yorkshire and The Humber). So they don’t consider that the trend was decreasing in any English region. The positivity estimates across different regions are more similar than they were a few weeks ago – the estimates are between 1 in 45 and 1 in 55 testing positive in seven of the nine regions, but rather lower in the other two (South East, and London), where the latest estimates are 1 in 75. However, many of the margins of error for the regions overlap.

Further information

“I should point out that, on the face of it, it looks as if the ONS positivity estimate for the school years 7 to 11 age group fell in the latest week compared to the previous week. Last week’s ONS bulletin estimated the rate in that group as about 1 in 10, and this week’s estimate is about 1 in 15. However, ONS do revise their estimates for individual age groups as they obtain more data, and in fact, this week, they revised the estimate for the previous week for this group down to 1 in 15. ONS round these ‘1 in so many’ estimates to the nearest 5, and the revised estimates for last week and this week rounded to the nearest whole number are 1 in 14 and 1 in 13. So ONS are still estimating a small increase in the positivity rate in this age group over the most recent week (because 1 in 13 testing positive is a higher rate than 1 in 14 testing positive).”


Prof Jim Naismith, Director of the Rosalind Franklin Institute, and Professor of Structural Biology, University of Oxford, said:

“Today’s ONS figures for week ending 16th October are not good news. Prevalence in England has continued to increase (1 in 60 to 1 in 55).

“Scotland’s prevalence has continued to fall (1 in 80 to 1 in 90),

“These data are the most valuable resource we have for judging the virus. The day to day results are a poor indicator.

“The power of the vaccines can be seen in the much lower death and hospitalisation rate that this high level of infections is currently causing.

“This is the benefit of science, without vaccines the NHS would likely have had to triage, the economy would have suffered from a prolonged lock down and we would be facing a bleak winter.

“UK science has delivered clinical trials that introduced dexamethasone, tracked variants, studied their effects and pioneered new therapies. This is what science investment has meant and will mean for the UK.

“The peak in Scotland in early September was around 1 in 45. I pointed out at the time that this would be a reasonable guess at where England was headed. If correct, then we can expect more cases in England as it approaches its peak. I suggested that 1 in 45 might indicate a rough ceiling for the viral prevalence if all stayed the same.

“Nothing stays the same and there are changes.

“There is evidence of slight waning of immunity. Vaccines are extremely effective at preventing deaths and hospitalisation; they are less good at preventing infection. Even extremely effective is not perfect. A slight decrease in immunity still means you are protected against the worst of the disease but might lead to an increase in cases. For those offered a booster (third) jab, science shows it is incredibly effective. I would advise taking it immediately it is offered. For those who have not had their first jab, they are almost certain to contract covid19 if they have not already done so.

“There is a concern about the delta plus strain, a 10 % increase in transmissibility is bad news but to be expected. This is evolution at work, the more the virus circulates, the more it will randomly sample mutations and find those that help it spread.

“The change from the original to Delta strain was a much bigger leap, if confirmed a 10 % change in transmissibility with Delta plus makes things worse for case numbers. It does not seem that it is more deadly.

“A big change is the return to indoors as winter arrives, this will tend to increase the spread. The continued (albeit slow) fall in Scotland’s prevalence is encouraging. Increasing vaccine coverage will tend to decrease the spread of the virus, we can do better.

“It is depressing to see individual country’s performance against the virus treated like the World Cup; its not a competition. All lives have value and their loss is a heart break. Each country has made good and bad decisions, the trick is to stop what is wrong, keep what is right and identify what has worked elsewhere and implement it. The initial roll out of the vaccine is a UK success story for which much credit belongs to the government. Other countries learned from this. However, this success has meant that perhaps we have been too slow to learn from other country’s subsequent successes. For example, case numbers are growing across the EU, biology is not a branch of geography, the virus does what it does. However, the UK with 681 cases per 1M each day compares to the EU 175 , France, 73, German 153, Italy 47 and Spain 40. This has given these countries time and a margin for error. The French, Spanish and Italian roll out has now passed the UK in terms of % fully covered (67.4, 79.5, 70.5 vs 66.7%), Germany and the EU bloc have nearly caught up (65.5 %, 64.5%).

“The UK has decided to run at a high number of daily cases since the summer. This means we are deciding to immunise significant numbers of people by infection rather than vaccination. This is seen in increased death and long covid19 in the UK compared to other countries. It does mean that immunity will be higher than simply relying on the vaccine alone. In a democracy, politicians not scientists take these decisions.

“We are seeing around 1000 people a week die from covid19, this will rise. It seems fairly certain we will reach and exceed 1000 people a day admitted to hospital. I am not an expert on NHS capacity and this is well below the surge 4000 a day we hit last winter (where we came close to collapse). However, a constant high demand can wear things out just as a surge can burst them.

“Vaccinating teens is a sure way to decrease the load in the wider population, since the burden in this age group is extremely high (around 8%)

“Individual mask wearing, on its own, helps only a little. It is effective when part of a package of measures (ventilation, testing, distancing) and when it is universal.”



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic.  My quote above is in my capacity as an independent professional statistician.”

None others received.

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